Required ventilation airflow from ACH: Checking required ventilation airflow — Worked Scenario

What this scenario actually checks

Air changes per hour (ACH) expresses how many room volumes of air are supplied or exchanged each hour. This tool multiplies floor area by ceiling height to estimate room volume, then multiplies that volume by a target ACH to estimate airflow. It reports both m³/h and L/s for equipment comparisons. You must select the target ACH based on the actual occupancy, use and applicable standards; this calculator does not determine a legally sufficient ventilation rate.

This walkthrough focuses on checking required ventilation airflow. It follows the published tool inputs, not a new formula or an automatically verified legal, financial, medical or engineering determination.

Start by preparing the right inputs

Measure the room's approximate floor area in m² and its effective height in metres; their product is the geometric room volume in m³. Enter the target air changes per hour (ACH) that you have independently selected for the space and intended use.

Before copying the example, confirm that each entered unit, date, dimension and default matches your real task. Changing only a visible number without revisiting its assumptions can change what the answer means.

• Measure the room's approximate floor area in m² and its effective height in metres; their product is the geometric room volume in m³.
• Enter the target air changes per hour (ACH) that you have independently selected for the space and intended use.
• Required airflow = area × height × ACH (m³/h). Divide m³/h by 3.6 to convert the result to litres per second (L/s).

Worked example with the calculator

Use the following input values: Floor area: 60 m²; height: 2.7 m; target: 4 ACH.

The example output is Room volume 162 m³; airflow 648 m³/h; 180 L/s. 60 × 2.7 = 162 m³. Four theoretical room air changes each hour require 162 × 4 = 648 m³/h.

For comparison, the same tool also documents these inputs: Floor area: 35 m²; height: 3 m; target: 6 ACH. Its result is Room volume 105 m³; airflow 630 m³/h; 175 L/s. A smaller room with a higher target ACH can require comparable airflow; 35 × 3 × 6 = 630 m³/h.

What can change the answer

Required airflow = area × height × ACH (m³/h). Divide m³/h by 3.6 to convert the result to litres per second (L/s). Check outdoor-air requirements, air distribution, duct pressure losses, filtration and equipment performance separately before specifying a fan or ventilation system.

Does ACH by itself prove adequate fresh-air ventilation? No. Recirculated airflow and outdoor-air supply are not interchangeable, and occupancy-based or contaminant-based requirements may control the design.

Why might the installed fan need a different rating? Published fan airflow can change with duct resistance, filters and installation conditions. Verify performance at the relevant static pressure and check air distribution.

Before using the result for a real decision

For checking required ventilation airflow, check the original measurements and input units, and save the assumptions alongside any number you share.

Where legal rules, official allowances, equipment ratings or contractual conditions matter, consult their current authoritative documents. An illustrative estimate is not a substitute for that verification.

• Reproduce the example before changing inputs
• Check all units and assumptions, including any default values
• Verify official or manufacturer-specific requirements outside the calculator